Reverse osmosis (RO) system is a water purification technology which can remove ions, molecules and particles from drinking water so as to provide clean and safe water for users. However, the process of reverse osmosis system may discharge a large amount of wastewater, which has lower quality and cannot be used directly for washing purpose. Although some user will place a water container to accumulate wastewater for gardening or flushing the toilet afterwards, it is troublesome and low efficiency to manually dispose wastewater. Therefore, there remains a need for a new and improved design for a reverse osmosis system to overcome the problems presented above.